Recently, chemists have sought to synthesize oligomers for high performance advanced composites suitable for aerospace applications. These composites should exhibit solvent resistance; be tough, impact resistant, and strong; be easy to process and be thermoplastic. Oligomers and composites that have thermo-oxidative stability and, accordingly, can be used at elevated temperatures are particularly desirable.
While epoxy-based composites are suitable for many applications, their brittle nature and susceptibility to thermal or hydrolytic degradation make them inadequate for many aerospace applications, especially those applications which require thermally stable, tough composites. Accordingly, research has recently focused on polyimide composites to achieve an acceptable balance between thermal stability, solvent resistance, and toughness. Still the maximum temperatures for use of the polyimide composites, such as PMR-15, are about 600.degree.-625.degree. F., since they have glass transition temperatures of about 690.degree. F. PMR-15, however, suffers from brittleness.
There has been a progression of polyimide sulfone compounds synthesized to provide unique properties or combinations of properties. For example, Kwiatkowski and Brode synthesized maleic-capped linear polyarylimides as disclosed in U.S. Pat. No. 3,839,287. Holub and Evans synthesized maleic- or nadic-capped, imido-substituted polyester compositions as disclosed in U.S. Pat. No. 3,729,446. We synthesized thermally stable polysulfone oligomers as disclosed in U.S. Pat. No. 4,476,184 or U.S. Pat. No. 4,536,559, and have continued to make advances with polyetherimidesulfones, polybenzoxazolesulfones, polybutadienesulfones, and "star" or "star-burst" multidimensional oligomers. We have shown surprisingly high glass transition temperatures yet reasonable processing and desirable physical properties in many of these oligomers and their composites.
Polybenzoxazoles, such as those disclosed in our copending applications U.S.S.N. 116,592 (to Lubowitz & Sheppard) and 121,964 (to Lubowitz, Sheppard, and Stephenson), may be used at temperatures up to about 750.degree.-775.degree. F., since these composites have glass transition temperatures of about 840.degree. F. Some aerospace applications need composites which have even higher use temperatures while maintaining toughness, solvent resistance, ease of processing, formability, strength, and impact resistance.
Multidimensional oligomers, such as disclosed in our copending applications U.S.S.N. 810,817 and 000,605, are easier to process than some advanced composite oligomers since they can be handled at lower temperatures. Upon curing, however, the oligomers crosslink (homopolymerize) through their end caps so that the thermal resistance of the resulting composite is markedly increased with only a minor loss of stiffness, matrix stress transfer (impact resistance), toughness, elasticity, and other mechanical properties. Glass transition temperatures above 950.degree. F. are achievable.
Commercial polyesters, when combined with well-known diluents, such as styrene, do not exhibit satisfactory thermal and oxidative resistance to be useful for aircraft or aerospace applications. Polyarylesters are often unsatisfactory, also, since the resins often are semicrystalline which may makes them insoluble in laminating solvents, intractable in fusion, and subject to shrinking or warping during composite fabrication. Those polyarylesters that are soluble in conventional laminating solvents remain so in composite form, thereby limiting their usefulness in structural composites. The high concentration of ester group contributes to resin strength and tenacity, but also makes the resin susceptible to the damaging effects of water absorption. High moisture absorption by commercial polyesters can lead to distortion of the composite when it is loaded at elevated temperature.
High performance, aerospace, polyester advanced composites, however, can be prepared using crosslinkable, end capped polyester imide ether sulfone oligomers that have an acceptable combination of solvent resistance, toughness, impact resistance, strength, case of processing, formability, and thermal resistance. By including Schiff base (--CH.dbd.N--), imidazole, thiazole, or oxazole linkages in the oligomer chain, the linear, advanced composites formed with polyester oligomers of our copending application U.S.S.N. 726,259 can have semiconductive or conductive properties when appropriately doped.
Conductive and semiconductive plastics have been extensively studied (see, e.g., U.S. Pat. Nos. 4,375,427; 4,338,222; 3,966,987; 4,344,869; and 4,344,870), but these polymers do not possess the blend of properties which are essential for aerospace applications. That is, the conductive polymers do not possess the blend of (1) toughness, (2) stiffness, (3) elasticity, (4) ease of processing, (5) impact resistance (and other matrix stress transfer capabilities), (6) retention of properties over a broad range of temperatures, and (7) high temperature resistance that is desirable on aerospace advanced composites. The prior art composites are often too brittle.
Thermally stable multidimensional oligomers having semiconductive or conductive properties when doped with suitable dopants are also known and are described in our copending applications (including U.S.S.N. 773,381 to Lubowitz, Sheppard and Torre). The linear arms of the oligomers contain conductive linkages, such as Schiff base (--N.dbd.CH--) linkages, between aromatic groups. Sulfone and ether linkages are interspersed in the arms. Each arm is terminated with a mono- or difunctional end cap (i.e. an end cap having one or two crosslinking functionalities) to allow controlled crosslinking upon heat-induced or chemically-induced curing. Other "semiconductive" oligomers are described in our other copending applications.
Polyamide oligomers and blends are described in our copending applications U.S.S.N. 046,202 and 051,884, and polyetherimide oligomers and blends are described in our copending application U.S.S.N. 016,703.
Polyamideimides are generally injection-moldable, amorphous, engineering thermoplastics which absorb water (swell) when subjected to humid environments or immersed in water. Polyamideimides are generally described in the following patents: U.S. Pat. Nos. 3,658,938; 4,628,079; 4,599,383; 4,574,144; or 3,988,344. The thermal integrity and solvent-resistance can be greatly enhanced by capping amideimide backbones with monomers that present one or two crosslinking functionalities at each end of the oligomer, as described in our copending application U.S.S.N. 092,740.
In all of these cases, the advantages are achieved by use of unsaturated hydrocarbon radicals at the ends of the polymeric backbones, which crosslink by addition polymerization when the oligomers are cured. The radicals (D) generally are selected from the group consisting of: ##STR3## wherein R.sub.1 =lower alkyl, lower alkoxy, aryl, substituted aryl, substituted alkyl (including hydroxyl or halo substitutents), aryloxy, halogen, or mixtures thereof;
j=0, 1, or 2; PA0 Me=methyl; PA0 G=--SO.sub.2 --, --CH.sub.2 --, --S--, --O--, --CO--, --SO--, --CHR--, or --CR.sub.2 -- (preferably --CH.sub.2 -- or --O--); PA0 E=methallyl or allyl; and PA0 R=hydrogen, lower alkyl, or phenyl. PA0 Y is selected from the group consisting of: ##STR4## i is 2, Ar is ##STR5## and B is --OH or halogen. PA0 j=0, 1, or 2; PA0 Me=methyl; PA0 G=--SO.sub.2 --, --CH.sub.2 --, --S--, --O--, --CO--, --SO--, --CHR--, or --CR.sub.2 -- (preferably --CH.sub.2 -- or --O--); PA0 E=methallyl or allyl; and PA0 R=hydrogen, lower alkyl, or phenyl, PA0 R.sub.3 =hydrogen, lower alkyl, or aryl (and, preferably, hydrogen) PA0 imidesulfone; PA0 ether PA0 ethersulfone; PA0 amide; PA0 imide; PA0 ester; PA0 estersulfone; PA0 etherimide; PA0 amideimide; PA0 oxazole; PA0 oxazole sulfone; PA0 thiazole; PA0 thiazole sulfone; PA0 imidazole; and PA0 imidazole sulfone, PA0 amideimide/imide; PA0 amideimide/imidesulfone; PA0 amideimide/heterocycle; PA0 amideimide/heterocycle sulfone; PA0 imide/heterocycle; PA0 imidesulfone/heterocycle; PA0 imide/heterocycle sulfone; PA0 imide/amide; PA0 imidesulfone/amide; PA0 ester/amide; PA0 estersulfone/amide; PA0 ester/imide; PA0 ester/imidesulfone; PA0 estersulfone/imide; or PA0 estersulfone/imidesulfone. PA0 i=1 or 2; PA0 A=a hydrocarbon residue, preferably from one of the families previously described and having an aromatic, aliphatic, or aromatic and aliphatic backbone; and PA0 D=an unsaturated hydrocarbon radical that is suitable for crosslinking, and generally includes the residue of a pyrimidine-based end cap that has previously been described. PA0 i=1 or 2; PA0 A=a hydrocarbon backbone; and PA0 D=an unsaturated hydrocarbon residue as previously described, but perferably one selected from the group consisting of: ##STR11## G=--SO.sub.2 --, --S--, --O--, CO--, or --CH.sub.2 --; and R=hydrogen, lower alkyl, or phenyl PA0 i=1 or 2; PA0 B=a hydrocarbon backbone that is from the same or a different chemical family as A; and PA0 Z=a hydrocarbon residue including a segment selected from the group consisting of: ##STR12## X=--O-- or --S--. The backbones (A or B) in this circumstance of coreactive oligomer blends, as with the pure component oligomers, are generally individually selected from the group consisting of: PA0 imidesulfones; PA0 ethersulfones; PA0 amides; PA0 ethers; PA0 esters; PA0 estersulfones; PA0 imides; PA0 etherimides; PA0 amideimides; PA0 oxazoles; PA0 thiazoles; PA0 imidazoles, or PA0 heterocycle (i.e. oxazole, thiazole PA0 imidazole) sulfones; PA0 G=--SO.sub.2 --, --S--, --O--, --CO--, --CH.sub.2 --, --SO--, --CHR--, or --CR.sub.2 --; PA0 R=hydrogen, lower alkyl, or phenyl; PA0 W=--OH, or --X; and PA0 X=halogen. PA0 R.sub.2 =a trivalent organic radical, and preferably phenyl. PA0 R.sub.2 =a trivalent organic radical, and preferably phenyl; PA0 R.sub.3 =an aromatic, aliphatic, or alicyclic radical, and preferably a phenoxyphenyl sulfone. PA0 R.sub.4 =a divalent organic radical; PA0 M=a small integer, usually from 0-5, but generally sufficiently large to impart thermoplastic properties in the oligomer; PA0 .phi.=phenyl; and PA0 i=1 or 2. PA0 m=a small integer; and PA0 D=--CO--, --SO.sub.2 --, --(CF.sub.3).sub.2 C-- or mixtures thereof. PA0 2,2-bis-(4-hydroxyphenyl)-propane (i.e., bisphenol-A); PA0 bis-(2-hydroxyphenyl)-methane; PA0 bis-(4-hydroxyphenyl)-methane; PA0 1,1-bis-(4-hydroxyphenyl)-ethane; PA0 1,2-bis-(4-hydroxyphenyl)-ethane; PA0 1,1-bis-(3-chloro-4-hydroxyphenyl)-ethane; PA0 1,1-bis-(3,5-dimethyl-4-hydroxyphenyl)-ethane; PA0 2,2-bis-(3-phenyl-4-hydroxyphenyl)-propane; PA0 2,2-bis-(4-hydroxynaphthyl)-propane PA0 2,2-bis-(4-hydroxyphenyl)-pentane; PA0 2,2-bis-(4-hydroxyphenyl)-hexane; PA0 bis-(4-hydroxyphenyl)-phenylmethane; PA0 bis-(4-hydroxyphenyl)-cyclohexylmethane; PA0 1,2-bis-(4-hydroxyphenyl)-1,2-bis-(phenyl)-ethane; PA0 2,2-bis-(4-hydroxyphenyl)-1-phenylpropane; PA0 bis-(3-nitro-4-hydrophenyl)-methane; PA0 bis-(4-hydroxy-2,6-dimethyl-3-methoxyphenyl)-methane; PA0 2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane; PA0 2,2-bis-(3-bromo-4-hydroxyphenyl)-propane; PA0 q=--S--, --SO.sub.2 --, --CO--, --(CH.sub.3).sub.2 C--, and --(CF.sub.3).sub.2 C--, and preferably either --SO.sub.2 -- or --CO--. PA0 (a) phenyl; PA0 (b) naphthyl; PA0 (c) biphenyl; PA0 (d) a polyaryl "sulfone" divalent radical of the general formula: ##STR27## wherein D=--S--, --O--, --CO--, --SO.sub.2 --, --(CH.sub.3).sub.2 C--, --(CF.sub.3).sub.2 C--, or mixtures thereof throughout the chain; or PA0 (e) a divalent radical having conductive linkages, illustrated by Schiff base compounds selected from the group consisting of: ##STR28## wherein R is selected from the group consisting of: phenyl; biphenyl; naphthyl; or a divalent radical of the general formula: ##STR29## wherein W=--SO.sub.2 -- or --CH.sub.2 --; and q=0--4; or (f) a divalent radical of the general formula: ##STR30## wherein R.sup.1 =a C.sub.2 to C.sub.12 divalent aliphatic alicyclic, or aromatic radical, and, preferably, phenyl (as described in U.S. Pat. No. 4,556,697). PA0 adipylchloride, PA0 malonyl chloride, PA0 succinyl chloride, PA0 glutaryl chloride, PA0 pimelic acid dichloride, PA0 suberic acid dichloride, PA0 azelaic acid dichloride, PA0 sebacic acid dichloride, PA0 dodecandioic acid dichloride, PA0 phthaloyl chloride, PA0 isophthaloyl chloride, PA0 terephthaloyl chloride, PA0 1,4-naphthalene dicarboxylic acid dichloride, and PA0 4,4'-diphenylether dicarboxylic acid dichloride. PA0 (a) pyromellitic dianhydride, PA0 (b) benzophenonetetracarboxylic dianhydride (BTDA), and PA0 (c) 5-(2,5-diketotetrahydrofuryl)-3-methylcyclohexene-1,2-dicarboxylic anhydride (MCTC), PA0 A.sub.1 = ##STR39## n=1 or 2; Z.sub.1 =D or Z, as previously defined; PA0 R=a trivalent C.sub.(6-13) aromatic organic radical; PA0 R.sub.1 =any of lower alkyl, lower alkoxy, aryl, substituted alkyl, or substituted aryl (including hydroxyl or halo substituents); PA0 R.sub.1 =a divalent C.sub.(6-30) aromatic organic radical; PA0 A.sub.2 = ##STR40## .phi.=phenyl. PA0 R'=a divalent C.sub.(6-30) aromatic organic radical, and PA0 M=an alkali metal ion or ammonium salt or hydrogen. PA0 L=--CH.sub.2 --, (CH.sub.3).sub.2 C--, --(CF.sub.3).sub.2 C--, --O--, --S--, --SO.sub.2 -- or --CO--; PA0 Ar'= ##STR48## Ar= ##STR49## T and T.sub.1 =lower alkyl, lower alkoxy, aryl, aryloxy, substituted alkyl, substituted aryl, halogen, or mixtures thereof; PA0 q=0-4; PA0 k=0-3; and PA0 j=0, 1, or 2. PA0 biphenyl; PA0 naphthyl; or PA0 a radical of the general formula: ##STR51## wherein W=--CH.sub.2 -- or --SO.sub.2 --; or a dialcohol selected from the group: ##STR52## wherein L is as previously defined; PA0 Me=methyl; PA0 m=an integer, generally less than 5, and preferably 0 or 1; and PA0 D=any of --CO--, --SO.sub.2 --, or --(CF.sub.3).sub.2 C--. PA0 y=1 to 5. PA0 (a) 2 moles of a hydroxyl end-cap monomer; PA0 (b) n moles of a four-functional compound, and PA0 (c) (n+1) moles of a suitable dicarboxylic acid halide, PA0 (a) 2 moles of an acid halide end-cap monomer; PA0 (b) (n+1) moles of a four-functional compound; and PA0 (c) n moles of a dicarboxylic acid halide. PA0 Y=--OH, --SH, or --NH.sub.2. PA0 A.sub.2 =a crosslinking end cap as previously defined. PA0 (a) unstable in air; PA0 (b) unstable at high temperatures; PA0 (c) brittle after doping; PA0 (d) toxic because of the dopants; or PA0 (e) intractable.
The radicals can be the residue of an anhydride that is reacted with an amino-terminated polymeric backbone (or be included in the reaction mixture of polymeric precursors used for synthesizing such a backbone) or can be condensed with aminophenol, nitroaniline, aminobenzoic acid, diaminophenol, diaminobenzoic acid or the like to form a mono- or difunctional end-cap monomer.